Gaseous Analysis Flashcards
I got some gas that needs analyzin'!
Oxygen Analysis types (5)
Galvanic (electrogalvanic) fuel cell
Polarographic electrode (Clark electrode)
Paramagnetic Oxygen sensor (Magnetomechanical “Dumbbell Principle)
Fluorescence-quenching
pH Optode
CO2 Analyzers (3)
Severinghaus PCO2 electrode
Fluorescence-quenching
pH Optode (optic)
Organic and Inorganic Gas Analysis (6)
Gas-Liquid Chromatography Infrared Analysis Mass Spectrometry Raman Scattering Piezoelectric Analysis Interferometry-Refractomer
Galvanic (electrogalvanic) fuel cell
Called a fuel cell because the reaction that takes place creates its own electric current by consuming its fuel.
The electrogalvanic sensor has a membrane permeable to gases but not liquids.
At the anode electrons are liberated in an oxidative reaction. The meter measures the current produced by the electrons consumed in the reaction at the cathode. The electron flow between the anode and the cathode is directly proportional to oxygen concentration
Polarographic electrode (Clark electrode)
Consists of a voltage source and a current meter connected to a platinum cathode and a silver anode.
A membrane permeable to oxygen covers one surface of the cell. A polarizing voltage is applied between the electrodes.
At the anode electrons are liberated by oxidative reaction, the meter measures the current produced by electrons consumed in the reaction at the cathode. Current flow in proportional to oxygen concentration.
Paramagnetic Oxygen sensor
Uses oxygen molecules’ unique attraction into magnetic fields. The parametric oxygen sensor is constructed with two nitrogen-filled bulbs attached together by a stem; this resembles a dumbbell. This dumbbell shaped apparatus is suspended parallel to a magnetic field in its “at-rest” state. The introduction of oxygen into this sensor causes the dumbbell oxygen apparatus to be displaced out of the magnetic field as oxygen is attracted into the field. The amount of displacement of the dumbbell apparatus is directly proportional to the concentration of oxygen.
Fluorescence-quenching (oxygen and CO2)
Fluorescence is caused by a molecule emitting light in response to being energized, causing an electron to bounce up to a higher energy level. The energized (excited) electron then returns to its lower energy level (resting state) by releasing a photon (spontaneous emission). The released photon is observed as light, with its color representing the emitted photon’s frequency. Fluorescence quenching uses oxygen’s ability to suppress, or quench, certain molecules from fluorescing. When a fluorescent molecule is excited to a higher energy state it will emit a photon. Oxygen, if present, will absorb this photon and prevent its release. The amount of fluorescence quenched is directly proportional to the concentration of oxygen present.
In relation to CO2 analysis the CO2 is not a quencher of fluorescence but rather the CO2 causes a change in the PH, by liberating H ions which react with the quenching agent or a fluorescent dye in the CO2 sensor. The resulting fluorescence is altered proportionally to the concentration of CO2.
pH Optode (oxygen and CO2)
Utilizes the florescence-quenching principle applied to hydrogen ions
pH changes the energy transfer. Changes in pH changes the color or luminescence of the gas.
Severinghaus PCO2 electrode
A system that uses a pH sensitive electrode immersed in a bicarbonate solution with a gas permeable membrane. CO2 diffuses into the sensor and is converted into free H+ ions, generating a current of electrical charge. The current is thus proportional to the CO2 concentration.
Advantages:
- Can selectively measure CO2 partial pressure in liquid or gas phase.
- Used in ABG analysis
Disadvantages:
-lag time 1-2 minutes
Gas-Liquid Chromatography
Mentioned briefly in powerpoint saying it deals with mixtures and it separates them based on solubility of components
Also that a voltage is applied and that voltage varies on the substance. Useful really for trace gases and does not give a continuous reading.
Infrared Analysis
Infrared analysis uses the ability of each of the anesthetic gases to absorb specific IR frequencies. A sample of a gas or a mixture of gases is subject to a known range of infrared frequencies. The frequencies lost to absorption are measured and the identification of the gas or gases may be made by the specific frequencies each gas absorbs. Anesthetic agents’ infrared absorptions are unique but close in frequency.
Newer infrared absorption analysis monitors are capable of identifying specific agents without preprogramming the specific agents.
Mass Spectrometry
Outdated method of anesthetic agent monitoring. It involves one large central machine, placed in its own dedicated equipment room in the OR. Sample lines from each anesthesia machine are piped to the central analyzer and the anesthetist pushes a button in his/her room to obtain a gas analysis. The machine can analyze only 1 room’s sample at a time so there may be a delay of 2-10 min as the machine analyzes submitted requests in the order they are received.
It works by ionizing the sample gas and passing it through a magnetic field. Each gas hurdles through the magnetic field at a different trajectory – gases with lighter molecular weights like Desflurane are more easily deflected in the magnetic field than heavier gases like Sevo. Individual detectors are located at the end of the field to detect specific gases along their unique trajectory.
Advantages: one unit to maintain and calibrate, lower $ to operate, analyzes ALL gases, can detect combinations of inhalation agents
Disadvantages: slow, NO continuous readings, measures only pre-programmed gases, malfunction shuts down all monitoring, requires large dedicated room to house machine
Raman Scattering
Gas analysis using electromagnetic radiation with matter. Passes a monochromatic laser beam through a gas mixture, causing an increased vibration frequency of the excited gas molecules. When the laser beam interacts with the anesthetic gas it may be absorbed, or scattered. Each anesthetic gas scatters laser frequencies uniquely. The spectral analysis is represented as Stokes lines. Raman scattering analyzers return the sample to the patient circuit, and do not need scavenging.
Not good with pediatrics due to high carrier gas rates and low tidal volumes.
Piezoelectric Analysis
A piezoelectric crystal will vibrate at a set frequency when an electric current is applied to it. A vibrating piezoelectric crystal coated with a liquid solution will alter its resonant frequency when exposed to a gas. As a gas dissolves into the liquid, in proportion to its concentration above the liquid gas interphase, the resonant frequency of the crystal is altered. The degree of frequency change is proportional to the concentration of gas that is dissolved into the liquid. The amount of gas that dissolves into the piezoelectric crystal’s liquid coating is directly related to the partial pressure of that gas (Henry’s Law).
Disadvantage: does not identify the specific anesthetic agent.
Interferometry-Refractomer
Interferometry is the measurement of the resulting sine wave when two sine waves “interfere” with one another. A light beam (sine waves) passed through a gas will be slowed by molecular collisions and the measured light waveform will be altered.
- An unaltered reference light beam when added to the altered light beam will show a spectrum shift when viewed through a refractometer
- Measures concentration only, does not identify gases
